ffmpegthumbnailer: enable generation of thumbnailer file, misc cleanups

Passing "-DENABLE_THUMBNAILER=ON" to CMake causes it to install
"ffmpegthumbnailer.thumbnailer" into /share/thumbnailers, making it
actually usable with desktop environments.

Cleanups:
- remove trailing whitespace
- change pkgconfig -> pkg-config
- change license from gpl2 to gpl2Plus

(cherry picked from commit 6a4695b)

pkgs/development/libraries/ffmpegthumbnailer/default.nix

@@ -1,4 +1,4 @@
-{ fetchFromGitHub, stdenv, ffmpeg_3, cmake, libpng, pkgconfig, libjpeg
+{ fetchFromGitHub, stdenv, ffmpeg_3, cmake, libpng, pkg-config, libjpeg
 }:
 
 stdenv.mkDerivation rec {
@@ -12,13 +12,14 @@ stdenv.mkDerivation rec {
     sha256 = "1bakbr714j7yxdal1f5iq0gcl4cxggbbgj227ihdh5kvygqlwich";
   };
 
-  nativeBuildInputs = [ cmake pkgconfig ];
+  nativeBuildInputs = [ cmake pkg-config ];
   buildInputs = [ ffmpeg_3 libpng libjpeg ];
+  cmakeFlags = [ "-DENABLE_THUMBNAILER=ON" ];
 
   meta = with stdenv.lib;  {
     homepage = "https://github.com/dirkvdb/ffmpegthumbnailer";
     description = "A lightweight video thumbnailer";
-    longDescription = "FFmpegthumbnailer is a lightweight video 
+    longDescription = "FFmpegthumbnailer is a lightweight video
         thumbnailer that can be used by file managers to create thumbnails
         for your video files. The thumbnailer uses ffmpeg o decode frames
         from the video files, so supported videoformats depend on the
@@ -27,7 +28,7 @@ stdenv.mkDerivation rec {
         The only dependencies are ffmpeg and libpng.
     ";
     platforms = platforms.linux;
-    license = licenses.gpl2;
+    license = licenses.gpl2Plus;
     maintainers = [ maintainers.jagajaga ];
   };